The present invention relates to the field of injection molding machines and, more particularly, to improvements in a take-out device for removing hot molded articles, such as preforms, from the molds, cooling them, and then discharging the cooled articles onto a conveyor or other handling equipment. The present invention is particularly concerned with an improved way of ejecting the cooled articles from the take-out device by pneumatic pressure.
Robotic take-out devices for removing hot molded plastic articles such as PET preforms from molds when the molding machine is in a mold-open position and then cooling the preforms while they are carried to a take-out conveyor are well known in the art. An example of one such apparatus is disclosed in U.S. Pat. No. Re. 33,237. The take-out device disclosed in the ""237 patent relies upon a positive pressure air system to eject the preforms from the device after they have been cooled. One problem with a system of that type, however, is that certain of the cooled preforms may stick in their cooling tubes while others may freely eject. Once some of the preforms have ejected, there may be insufficient air pressure at the sticking preforms to dislodge them from their tube because the air system is effectively vented to atmosphere at the numerous empty tubes.
One way to avoid the venting problem is to provide positive mechanical ejection of the preforms. See, for example, U.S. Pat. No. 5,447,426 disclosing the use of mechanical ejector bars that, when operated, engage the undersides of neck flanges on the preforms and pull the preforms out of the cooling tubes. Other types of mechanical ejector mechanisms are also well-known in the art. However, the known mechanical ejector mechanisms are generally more complex than air ejector systems and have the disadvantage of increasing the number of operating components involved, which necessarily increases costs and raises issues of mechanical reliability.
The present invention solves the sticking problem while providing a simple alternative to known mechanical ejectors. Instead of mechanical ejection, the present invention contemplates a return to pneumatic ejection but incorporates the additional feature of momentarily retaining all of the cooled preforms within their tubes by blocking their escape until they have been slightly dislodged by the initial application of positive pressure air. By keeping the preforms essentially in place until all have been dislodged, no significant venting to atmosphere takes place such that adequate air pressure is assured in those tubes where sticking might otherwise be a problem. Once dislodged, removal of the retaining structure allows the preforms to be blown out of the tubes by the air pressure.
In its preferred form, the present invention contemplates the use of a shiftable retainer plate that overlies the open ends of the cooling tubes. The plate is provided with a plurality of holes that are strategically located to be aligned or disaligned with the open ends of the cooling tubes, depending upon the position of the plate. In a closed position of the plate, enlarged pass-through portions of the holes are registered with the tubes so as to permit hot preforms to be received within the tubes from the molds of the molding machine. The plate is spaced slightly outwardly from the open ends of the tubes so that when the cooling preforms are within the tubes, the annular flanges on the preforms reside in the space between the tube and the plate while the necks of the preforms project out through the holes. When the plate is then shifted to its closed position, a smaller size blocking portion of each hole moves into embracing relationship with the neck while solid surfaces of the plate come into overlying relationship with the flanges of the preforms.
With the plate thus in its closed position, the introduction of pressurized air into the inner ends of the tubes causes the preforms to pop-out slightly in a dislodging motion until the flanges butt up against the plate. If any one or more of the preforms tend to stick in their tube, the fact that all of the preforms are still in their tubes, even though some are partially dislodged, means that no substantial venting to atmosphere occurs. Consequently, adequate air pressure is assured in the sticking tubes to dislodge even those preforms. After a momentary period of delay for dislodgement, the plate is shifted to its open position allowing the dislodged preforms to be ejected from the tubes by the air pressure.